1. Field of the Invention
The present invention generally relates to an oscillating actuator drive unit, a lens barrel, an optical apparatus, a method for adjusting a voltage, and a computer-readable recording medium.
Priority is claimed on Japanese Patent Application No. 2009-203697, filed Sep. 3, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In an autofocus driving mechanism equipped in a lens barrel of an optical apparatus of a camera or the like, an oscillating actuator such as an ultrasonic motor is used. The ultrasonic motor includes a stator having a piezoelectric element and a rotor for performing rotational motion. The rotor is rotated by applying alternating voltage (AC voltage) at a frequency more than a predetermined frequency to the piezoelectric element of the stator. In this case, an LC (an inductor-capacitor) resonant circuit is formed by the capacitance of the piezoelectric element and the inductance of a driving unit to which AC voltage is applied.
With recent progress on miniaturization of a camera or the like, the miniaturization of the ultrasonic motor equipped in the autofocus mechanism is also under progress. While the ultrasonic motor is miniaturized, the capacitance of the piezoelectric element of the ultrasonic motor fluctuates due to the fluctuation of manufacturing conditions (hereafter manufacturing fluctuation), and also the inductance of the driving unit fluctuates due to the manufacturing conditions. The manufacturing fluctuations of the capacitance of the piezoelectric element and the driving unit change a peak value of the AC voltage applied to the LC circuit, in other words, the peak voltage Vp-p of the AC voltage applied to the piezoelectric element of the ultrasonic motor is varied. As a result, for an ultrasonic motor whose driving velocity is controlled by the frequency of the AC voltage, the driving velocity of the ultrasonic motor fluctuates.
For the matter mentioned above, Japanese Unexamined Patent Application, First Publication, No. 2009-047791 describes that the fluctuation of the driving velocity of the ultrasonic motor is corrected by adjusting the frequency of the AC voltage applied to the piezoelectric element, so that the accuracy of the driving controllability of the ultrasonic motor is improved.
However, the method described in the patent publication does not reduce the fluctuation of the peak voltage Vp-p of the AC voltage applied to the LC resonant circuit consisting of the inductance of the piezoelectric element of the ultrasonic motor and the driving unit, in which the fluctuation of the peak voltage Vp-p of the AC voltage is caused by the manufacturing fluctuation of the piezoelectric element of the ultrasonic motor and the driving unit. When the peak voltage Vp-p of the AC voltage is increased, the power consumption of a circuit increases. For example, for a camera or the like which is driven with a battery, there is a problem that the operable time period becomes shorter.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.